1. Field of the Invention
This invention relates generally to a method and apparatus for relieving an excess negative pressure condition, and in particular to a negative pressure relief valve for automatically or manually relieving an excess negative pressure condition in a medical device. Specifically, the invention relates to a combination automatic/manual negative pressure relief valve having a moving diaphragm that permits ambient air to enter the suction side of the valve when negative pressure therein exceeds a predetermined threshold in order to relieve an excess negative pressure condition inside the medical device.
2. Prior Art
Negative pressure relief valves are well known in the medical art. Typically, such valves are incorporated in medical devices, such a chest drainage units (CDU), in order to protect the patient from possible tissue damage in the pleural cavity caused by an excess negative pressure condition generated inside the CDU. To protect the patient a negative pressure relief valve is sometimes housed on the outer wall of the CDU for permitting the venting in of ambient air in order to relieve an excess negative pressure that may build inside the CDU during operation.
A CDU is an apparatus for suctioning gases and liquids from the pleural cavity of a patient. The pleural cavity lies within the rib cage above the diaphragm and is surrounded by the pleural membrane. The pleural cavity contains both lungs, which in their normal expanded state fill the pleural cavity. Several conditions and diseases such as interventional surgery, trauma, emphysema and various infections can cause a build up of liquid and gases around the lungs in the intrapleural space. When this happens, it causes the lungs to collapse to a volume much less than that of the pleural cavity, thereby severely impairing breathing functions of the patient. The lungs can be re-expanded to their normal state to fill the pleural cavity by draining the liquid and gases from the intrapleural space using a medical device like a CDU. A typical CDU and its operation is disclosed in U.S. patent application Ser. No. 08/810,056 to Swisher et al. entitled "Chest Drainage Unit with Controlled Automatic Excess Negativity Relief Feature" and is herein incorporated by reference in its entirety. However, any kind of medical device that requires low negative pressure control, such as a Tracheo Gas Insufflation (TGI) Device, is felt to fall within the scope of the present invention.
During the suctioning of liquids and gases from the pleural cavity of a patient by the CDU, negative pressure inside the CDU can build up to dangerous levels due to excess vacuum being mistakenly applied to the CDU from a hospital vacuum source by a user or when a procedure called "milking" is performed to the transfer tubing attached to the CDU. "Milking" is accomplished by squeezing the portion of latex transfer tubing between the patient and the CDU adjacent the patient and running the fingers down along the tube toward the CDU. When the tube is thereafter released, in the absence of any venting of the CDU's collection chamber, a relatively high level of negative pressure will be reflected in the patient's pleural cavity causing the patient's tissue around the end of the catheter in the pleural cavity to be sucked into the holes of the catheter, thereby causing irritation and tissue damage.
Negative pressure relief valves are used as a safety mechanism for ensuring that negative pressure inside the CDU does not rise to dangerous levels. One type of prior art valve is disclosed in U.S. Pat. No. 4,372,336 to Cornell et al. entitled "Chest Drainage Unit". The valve disclosed in Cornell et al. is a manual relief valve that permits venting of the CDU's collection chamber by simply depressing a button located on the top portion of the valve for venting in atmospheric air into the CDU and lowering the negative pressure therein. However, the valve disclosed by Cornell et al. lacks any type of automatic feature that would permit excess negative pressure inside the CDU to be relieved automatically without manual intervention.
U.S. Pat. No. 4,605,400 to Kurtz et al. entitled "Surgical Drainage Apparatus" discloses an automatic excess negative pressure relief valve that automatically lowers excess negative pressure. The Kurtz et al. device is an adjustable umbrella valve that automatically opens to vent in ambient air into the CDU when negative pressure therein reaches a predetermined calibration point set for a biasing means. The biasing means, for example a helical spring, maintains the umbrella valve in a sealed position until the negative pressure inside the CDU reaches the calibration point. When the calibration point is reached, the pressure exerted by the ambient air overcomes the force applied by the biasing means to the valve, thereby opening the valve to atmosphere. As ambient air is allowed to bleed into the device it gradually lowers the negative pressure inside the CDU until it falls below the calibration point, whereupon the valve is again closed off to the inflow of ambient air into the CDU.
Unfortunately, the Kurtz et al. valve suffers from several drawbacks. As negative pressure inside the CDU nears the calibration point set for the valve, the Kurtz et al. device may begin to bleed in ambient air, thereby prematurely lowering the pressure inside the CDU. For example, an umbrella-type valve similar to that disclosed by Kurtz et al. may begin to prematurely leak and vent in ambient air as the umbrella valve begins to momentarily unseat, even though the negative pressure inside the CDU has not yet reached the set calibration point. Thus, the prior art umbrella valve may sometimes exhibit leakage which is undesirable. Moreover, the Kurtz et al. device lacks a combined valve that combines both an automatic means as well as a manual means of relieving an excess negative pressure condition inside the CDU.
An improvement on the above-noted umbrella valve is the use of a resilient diaphragm that hermetically separates the CDU into a venting side and a suction side. The suction side is the interior portions of the CDU and valve that are maintained at some negative pressure value while the venting side is that portion of the valve that is open to atmosphere. The diaphragm comprises an outer periphery and an inner periphery, wherein the inner periphery forms of the diaphragm is integrally attached or formed to a proximal end of a stem which is connected to a valve seat. The valve seat is normally seated and sealed against an opening that separates the venting side from the suction side, thereby preventing the inflow of ambient air into the suction side. A biasing means, for example a helical spring, biases the diaphragm so that the valve seat is seated against the opening. When the negative pressure inside the CDU rises and then exceeds the calibration point set for the biasing means, the biasing means begins to exert a specific pressure against the diaphragm in proportion to the amount of negative pressure generated in the suction side of the apparatus, thereby causing the diaphragm to flex. As the diaphragm flexes, it concurrently causes the stem to move in a direction that unseats the valve seat from the opening. Once the opening is unblocked it permits ambient air to flow from the venting side into the suction side, thus lowering the negative pressure inside the device. As negative pressure falls below the above-noted calibration point, the biasing means moves the diaphragm in a direction that forces the valve seat against the opening and closes it to fluid flow communication therethrough. However, this type of diaphragm valve also suffers from leakage since the valve seat configuration does not maintain a constant sealing force against the opening as the negative pressure inside the CDU nears the calibration point. Instead, the sealing force applied by the valve seat begins to drop off before the calibration point is reached, thereby permitting ambient air to prematurely vent into the suction side of the CDU.
As of yet, nothing in the prior art has addressed the problem of developing an excess negative pressure relief valve that prevents the leakage of ambient air through the valve mechanism when negative pressure inside the device has not reached or exceeded the calibration point set for the valve. Moreover, nothing in the prior art has addressed the need for an improved means of automatically actuating an excess negative pressure relief valve whereby the sealing force remains constant until the calibration point set for the biasing means is reached.